Indium and other trace elements in volcanogenic massive sulfide ores from the Kuroko, Besshi and other types in Japan

Abstract

By analyzing trace elements of massive sulfide ores from rhyodacite-related Kuroko deposits (35 samples) and Yanahara pyrite deposits (10 samples), andesite-related Taro deposits (4 samples), and basalt-related non-metamorphosed Shimokawa, Tsuchikura and Makimine deposits (6 samples) and metamorphosed Besshi-type deposits (25 samples), potentiality of indium resource was evaluated. In the major Hokuroku Basin for Kuroko deposits, those of the eastern side, such as the Kosaka-Uchinotai (avg. 26 ppm In), the Hanawa and Furutobe are relatively rich in indium, and the indium contents are correlated with not zinc but copper content. This indium may be contained in tetrahedrite-group minerals of the Kuroko horizon in a narrow sense. Based upon an average content of indium in the Kosaka-Uchinotai deposits and In-production in the 1970's, a recoverable amount in the Kosaka deposits is estimated to be 50 tons In, which are smaller two orders of magnitude than the world-class In-bearing massive sulfides deposits. On the contrary, In-anomalies are observed in the zinc concentrates of the Sazare and Shirataki mines, implying that indium in the Besshi-type deposits are mainly contained in sphalerites. Zinc grades of the crude ores of the Besshi-type deposits are low as 0.n% level. A large potentiality cannot be expected on the Besshi-type ore deposits. The high Invalues up to 207 ppm were obtained on the Cu-pyrrhotite-rich ores at Yanahara hosted in the Permian rhyolites. Sporadic In-anomalies, up to 167 ppm, have also been observed in ores from the thermally metamorphosed lower levels of the Besshi deposits. These are considered due to later hydrothermal In-enrichment along fractures by Miocene intrusion of the ilmenite series-granitoids of the Outer Zone of SW Japan.